This invention relates to video disc players and in particular to apparatus for the repeated replaying of a selected segment of signal recovered from a disc record.
Video disc records typically have information stored thereon in circular tracks or a continuous spiral track. The information is segmented into video fields, two fields when interlaced comprising a frame or one complete television picture. Each circular track or spiral convolution typically contains an integral number of frames, and the frames on adjacent tracks are typically aligned, i.e., the starting location and the terminal location of respective frames on adjacent tracks occur at the same angular coordinate of the disc.
Signal is recovered from the disc by a track following signal pickup transducer which may actually contact the disc as in the capacitive disc systems or may be removed from the disc as in the optical disc systems. In normal operation, playback is effected by rotating the disc to create relative disc-signal pickup transducer motion, the frames of signal information passing the transducer in an ascending succession as the transducer traces the track from convolution to convolution or is regularly displaced from circular track to circular track for each 360 degrees of disc rotation.
A freeze frame mode of operation is easily accomplished if the information tracks contain only one frame of information per track. By failing to advance the pickup transducer at the end of the track (concentric circular tracked disc) or by deflecting the pickup transducer back one track convolution (spiral tracked disc) the same frame is replayed as often as desired and thereby frozen. On the other hand, if each track contains more than one frame of information, replaying any particular track replays each of the frames in the track and unless each of the frames in the particular track is identical, some change or motion will occur in the displayed signal, producing an undesirable result. In order to effect freeze frame from discs having this last mentioned signal format, it becomes necessary to snatch the desired frame and put it in memory from which it can be repeatedly accessed, and replayed. The cost of most memory systems to accomplish such frame snatching is generally prohibitive to their use in consumer video disc players. The present invention, however, provides a low cost memory system for a video disc player to provide frame snatching for freeze frame or other special playback effects.